1. Field of the Invention
The present invention relates to an image processing system in which image data, as read by an image read section, is compressed and stored into a large capacity memory, the image data is read out of the memory and decompressed into the original image data, and the decompressed data is output to an image output section.
2. Discussion of the Related Art
A conventional RDH (recirculating document handler) repeatedly reads images from a plurality of documents in succession using an automatic document reader, and outputs a required number of copies. A more recently developed electronic RDH outputs a required number of copies after only reading the documents one time. The more recent electronic RDH employs a memory of large memory capacity, such as a hard disk and a semiconductor memory, for storing image data. To output a required number of copies, a plurality of documents are each read one time in successive order. Then, the image data as read are stored into the memory. The image data are repeatedly read out of the memory in sequential order, and transferred to the image output section. Finally, the required number of copies are output.
The image data contains a large amount of information, and, thus requires a large capacity memory to store the image data. To cope with this, a compressor and a decompressor (also called an "expander") are used. Before the image data is stored into the memory, it is compressed by the compressor. The image data as compressed and stored are read out of the memory and decompressed by the decompressor to restore the original data. The decompressed data is then transferred to the image output section.
Where a hard disk (HD) is used for the memory, time required to read image data out of the HD is longer than the time required for the decompressing processing image data and output processing by the decompressor and the image output section. To compensate for the timing difference, a page buffer is used. The image data is read out of the hard disk every page, and loaded into the page buffer. The image data is read out of the page buffer and transferred to the decompressor. The image data, as decompressed by the decompressor, is sent to the image output section, and is output in hard copy form. Operation of the electronic RDH will be described briefly below.
FIG. 1 shows a timing chart useful in explaining an operation of the electronic RDH. FIG. 2 shows a flow chart useful in explaining the output processing of a second and of subsequent copies.
When a copy start key is pressed, the electronic RDH starts scanning to read an image for the first copy, as shown in FIG. 1. The image data read are sequentially stored into a disk and are then output. FIG. 1 shows the scanning operation for an original having three pages. For the second and subsequent copies, the image data is read out of the disk successively from the first page to the last (page 3), and the images are output. The sequence of operations is repeated until designated number of copies is obtained.
The output processing of the second and subsequent copies will be described in detail with reference to FIG. 2. First, the number of copies is set to "1" (step S1). Next, the read page number is set to "1" (step S2), image data of one page are read out of the hard disk and stored into the page buffer (step S3), and the one-page data thus stored are transferred to the image output section (step S4). Next, it is determined whether or not the last page has been reached or completed (step S5). When the last page has not been reached, the page number is incremented by one (step S6), and step S3 and subsequent steps are re-executed. On the other hand, when the last page has been reached, the number of copies is incremented by one (step S7), and it is determined whether or not all copies has been completed (step S8). When all copies have not been completed, step S2 and subsequent steps are re-executed.
In the image processing system of the type in which image data is read out of the hard disk to the page buffer every page, and then is transferred to the image output section, control must wait until the reading of the image data from the hard disk is completed and before it transfers tho data to the output section. This wait time occurs for every page and slows the image outputting speed. When copying the second and subsequent documents, one cycle of the image outputting consists of the sum of the read-out time t.sub.R of the hard disk and the time to of the image outputting, t.sub.R +t.sub.o, as shown in FIG. 1. Therefore, the time taken to copy the documents of "n" pages is n.times.(t.sub.R +t.sub.o).
A method, illustrated in FIG. 4, has been proposed to cope with this problem. In FIG. 4, the transfer of the image data from the hard disk to the page buffer is continued without interruption until the image data of one page is completed, and subsequently the data transfer from the hard disk to the page buffer progresses concurrently with the data transfer from the page buffer to the image output section. This method, however, has the following problems:
(1) Because the read-out operation from the disk is uninterrupted, data cannot be written into the disk during the execution of parallel jobs.
(2) When the data is read out of the disk faster than the image outputting speed, the page buffer fills up with data and creates a bottleneck.